Circle of Confusion Calculator
Calculate the standard circle of confusion (CoC) value for common camera sensor formats or a custom sensor diagonal.
Result
Circle of Confusion
0.0289
mm
How to Use the Circle of Confusion Calculator
The circle of confusion (CoC) is the largest blur spot the human eye still perceives as an acceptably sharp point when viewing a print or screen at a normal distance. It scales with sensor size — smaller sensors need a smaller circle of confusion because their images are enlarged more to reach the same final output size. Pick a common sensor format preset, or enter a custom sensor diagonal in millimeters, to calculate the standard circle of confusion value for that sensor.
This 1/1500th-of-the-diagonal rule is a widely used photographic approximation that gives a practical, standardized CoC value for common depth-of-field calculations.
Example
A full-frame sensor has a diagonal of about 43.3mm, giving a circle of confusion of 43.3 ÷ 1500 ≈ 0.029mm (commonly rounded to 0.03mm). An APS-C sensor, with a smaller 28.2mm diagonal, has a smaller CoC of about 0.019mm, reflecting the fact that its images need more enlargement to reach the same output size.
Common Use Cases
- Finding the correct circle of confusion value to plug into a depth-of-field or hyperfocal distance calculator.
- Understanding why smaller sensors are rated with different CoC constants in photography references.
- Comparing the sharpness tolerance implied by different camera formats before buying gear.
FAQs
- How is this different from the Depth of Field Calculator? The Depth of Field Calculator computes near and far focus limits, and it needs a circle-of-confusion value as one of its inputs to do that. This tool is a companion calculator that figures out what that CoC value should actually be for your specific sensor format — use this one first, then feed the result into the depth-of-field calculation.
- Why isn't there one universal circle of confusion value for all cameras? Because sensor size determines how much an image must be enlarged to reach a standard viewing size (like an 8×10 print), and more enlargement makes any given blur spot more visible — so smaller sensors are assigned a proportionally smaller, stricter CoC value.
- Can I use a custom circle of confusion value instead of the standard one? Yes — some photographers use tighter custom CoC values for large prints or critical sharpness work. Enter your sensor's exact diagonal under "Custom" if you know it precisely, or adjust the resulting value manually for your own sharpness standard.